In recent years, as the development of power transistors has proceeded, efforts have been made to increase the performance of high-voltage semiconductor switching elements, such as a field-effect transistor (FET), an insulated gate bipolar transistor (IGBT), a high electron mobility transistor (HEMT) using a gallium nitride (GaN) layer as an electron transit layer, and so forth.
In a power transistor which is used for a switching power supply source, specifically, reducing a loss is an important challenge, and an on-resistance is used as an operation performance index for power transistors.
However, many of recent power transistors perform high-speed operation, and merely using an on-resistance calculated using DC characteristics is not enough as a performance index.
Thus, as an effective performance index used when a switching operation of a power transistor is performed, a dynamic on-resistance Ron is measured.
Referring to FIG. 1, in order to calculate the dynamic on-resistance Ron, a pulse voltage is input to a gate terminal of a power transistor, and calculation is performed, on the basis of an on-current Ids_on and an on-voltage Vds_on flowing in a drain at that time, using the dynamic on-resistance Ron=Vds_on/Ids_on.
FIGS. 2A-2D are charts illustrating waveforms obtained by calculating the switching loss and the dynamic on-resistance Ron from a drain voltage and a drain current when switching of the gate of a power transistor is performed.
In general, where the magnitude of the dynamic on-resistance Ron of a power transistor is dependent on a voltage (an off voltage Vds_off) which is applied when the power transistor is in an off state in many cases. A reason for this is that temperature that the transistor feels varies due to Joule heat generated by a switching loss caused by overlap of the waveform of a drain-source voltage Vds and the waveform of a drain-source current Ids with each other when switching from an off state to an on state or switching from an on state to an off state is performed and a conduction loss caused by Vds_on and Ids_on.
It is also known that, in a power transistor using a chemical semiconductor, current and voltage waveforms are dependent on Vds_off because of the electron and hole trapping level at which electrons and holes existing at a semiconductor surface and an interface are trapped.
The following is reference document:
[Document 1] Japanese Laid-open Patent Publication No. 2008-309702.